During general anesthesia, functional residual capacity (FRC) is reduced. If the FRC is lower than the minimum volume required to maintain the opening of the airways (closing capacity), there is a derecruitment of the lung parenchyma, leading to the phenomenon of expiratory flow limitation (EFL). Numerous factors contribute to the EFL, including hyperoxia, muscle paralysis, the increase of the volume of the interstitial fluids and the inflammatory response.